Smoking is the leading preventable cause of death in the U.S. A number of factor contribute to the challenge of quitting smoking, including the associative learning process whereby negative affect and stress-induced craving lead to smoking, and learned responses that are reinforced multiple times daily by smoking behavior. Many behavioral interventions have been developed to treat smoking, but success rates remain low. We have recently found that group-based mindfulness training, which specifically targets stress, craving and the learned responses, doubles abstinence rates compared to other behavioral treatments such as the American Lung Association's Freedom From Smoking. We have also found potential mechanisms for mindfulness training (MT): the decoupling of the link between craving and smoking. However, clinic group-based treatments are expensive and delivery is difficult to standardize due to variability in therapist experience and adherence to manualized training. Recent advances in mobile-phone applications have led to app-based interventions for smoking cessation that can reduce costs and optimize standardized delivery. To enhance delivery of MT, we have translated our manualized MT for smoking into a smartphone application (Craving To Quit, C2Q). Further, we have paired this with an online community, which can provide peer support and expert guidance. In the proposed study, The Primary Aim will assess the efficacy of mobile mindfulness training (C2Q). To achieve this, 1200 smokers will be randomized to receive C2Q, or The National Cancer Institute's NCIQuitPal. The primary endpoint will be self-reported 7-day point prevalence abstinence at 6 months after treatment initiation. Secondary Aim 1 will be to assess the short-term efficacy of the C2Q program. Secondary endpoints will include 7-day point prevalence abstinence at 3 months after treatment initiation. Secondary Aim 2 will be to determine the relationship between C2Q usage and tobacco abstinence at 3 and 6 months. C2Q program usage, measured by (1) the number of modules completed, (2) the amount of informal mindfulness practice completed, and (3) the number of visits to the online community will be used in regression analyses to determine the degree to which they predict smoking in the C2Q group. The proposed study provides potential benefits for society. First, this study will test the efficacy of a cost-effective treatment for smoking cessation, C2Q. Second, this study will test hypothesized predictors of outcomes which will improve our understanding and treatment of smoking cessation.